utils_test: Add two functions for libvirt tests

Function to check virsh commands exit status.
Function to check interface for virsh iface related tests.

Signed-off-by: Yanbing Du <ydu@redhat.com>

Conflicts:
	virttest/utils_test/libvirt.py
virttest.virsh: Add wrappers for iface related commands

Signed-off-by: Yanbing Du <ydu@redhat.com>
Typo fix

Signed-off-by: Yanbing Du <ydu@redhat.com>
.travis.yml: Tidy up requirements.txt and force pylint 1.0

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
documentation: .rst fixes

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest: Docstring fixes

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>